The present invention relates to a dry etching method, and particularly, to a dry etching method capable of selectively etching the desired material from a plurality of materials having different types of band gap energies or from a plurality of materials having different band gap energies.
The technique of selectively etching the desired material from a plurality of semiconductors having different compositions is very important in fabrication of a compound semiconductor device. For example, in fabrication of a semiconductor device having a heterostructure of GaAs and Al.sub.x Ga.sub.1-x As, Al.sub.x Ga.sub.1-x As is selectively etched by wet etching and GaAs is selectively etched by dry etching.
The selective wet etching of Al.sub.x Ga.sub.1-x As is conducted using an etchant of HCl/H.sub.2 O.sub.2 or NH.sub.3 /H.sub.2 O.sub.2 /H.sub.2 O. This is utilized in fabrication of a laser diode, HBT(Hetero-Bipolar Transistor) and the like. However, as is well known, the wet etching has such a problem as causing an under-cut and is thus unsuitable for fine patterning.
Meanwhile, a technique of selectively wet etching GaAs has not yet been found.
Japanese Journal of Applied physics Vol. 20, No. 11, pp. L847-L850 discloses that the selective dry etching of GaAs is possible by RIE (Reactive Ion Etching) using an etching gas of CCl.sub.2 F.sub.2. This depends on a non-volatile AlF.sub.3 formed on the surface of Al.sub.x Ga.sub.1-x As during etching. The non-volatile AlF.sub.3 obstructs the etching reaction, thereby reducing the etching rate of the Al.sub.x Ga.sub.1-x As. Meanwhile, such a thin film is not formed on the surface of GaAs, and thereby the etching rate of GaAs is relatively increased. However, it has not been realized to selectively dry etching only Al.sub.x Ga.sub.1-x As without etching GaAs.
As mentioned above, to selectively etch GaAs and Al.sub.x Ga.sub.1-x As, both the dry and wet etching techniques must be combined. However, since the wet etching is unsuitable for fine patterning, it is desired to selectively etch GaAs and Al.sub.x Ga.sub.1-x As by only dry etching.